Unable to install tomato on buffalo WHR-G54S

This is probably my 5th installation on Buffalo WRT devices.
I've never experienced any problem flashing the firmware from the original one to tomato before.
Basically what happens is that the whr_install.bat script is not working properly.
The router is booting up with the old firmware all the times.
I did set the IP of the LAN on 192.168.11.2/24
I did reset the default settings on the router, I did try to unplug/plug the power different times to help the script to kick in at the right moment... but no luck!

Is there any other way to flash the firmware?

I can access the original web console but I'm not sure I can flash the firmare with tomato from here.